In steel rolling, metal forming, and similar processes, gage variations which are induced in flat rolled sheet products by eccentricity of the back-up and/or work rolls, is a widespread problem which is growing in criticality as a result of increasing demand for improved control of gage variation and strip shape. Eccentricity is defined as the sum of out-of-roundness and concentricity errors, which can be quantified by total indicator run-out from a mean axis of rotation of the roll. The gage thickness of the final formed sheet is directly dependent upon the accuracy of the gage between opposed rollers and their eccentricity about their axis of rotation. Minimizing thickness variation in the sheet products is critical to enabling the most efficient use of materials and energy to produce acceptable products.
Current roll grinding and measuring technology has several deficiencies in providing roll roundness of sufficient accuracy to permit the precise control of strip gage variation required to produce flat rolled sheet products which meet the ever increasing tolerance demands of modern industry. These deficiencies include the fact that the accuracy of grinding the working surface of a roll can be no better than the roundness of the surfaces upon which the roll is supported during grinding procedures.
Large diameter back-up and work rolls used in steel making, aluminum processing, paper handling and similar applications conventionally include a cylindrical central work surface with oppositely disposed tapered neck portions extending longitudinally from either end, and cylindrical neck portions at the distal ends of the tapered portions. Grinding is most often undertaken while supporting the roll via its cylindrical neck portions. Additionally, due to the relatively large size of these rolls (e.g., as large as 60" in diameter, 15-20' in length, and weighing 50 tons or more), the rolls are often supported by Babbit support shoes, and the interface between the support shoes and the neck portions of the rolls is supplied with grease to reduce the frictional effects of the metal-to-metal contact. Inherently, however, such metal-to-metal contact can create frictional stick/slip interruptions in smooth rotation of the roll and which can be detrimental to uniform grinding operations.
In order for a grinding wheel to abrade the outer surface of a roll, substantial radial force must be imposed between that outer surface and the grinding wheel. In addition to and in combination with vibrations imposed by the ambient environment and the frictional effects of bearing supports and the like, the grinding force often varies and may become unstable, which can lead to chatter marks and other variations in the resulting roundness of the ground roll.
In addition to a need for improved machining apparatus to provide rolls with significant roundness characteristics, apparatus and procedures for accurately measuring the roundness of a roll prior to, during, and following grinding procedures must also be provided for determining the roundness of a particular roll at any particular time. The industry has experienced problems in the past in developing satisfactory roll calipers of manageable size and reasonable cost to ascertain the surface profile of roll diameters. Such calipers have often required inordinate amounts of time and manual operation to determine such a surface profile, as exemplified in the gaging devices of U.S. Pat. Nos. 2,019,066; 2,465,002; and 3,744,135.
An improved roll profile gage is shown in U.S. Pat. No. 4,524,546 (which issued to B. Hoover and the present applicant) contemplated for use with a conventional roll grinder having a headstock and tailstock for mounting the opposite ends of the roll to be ground. While the roll profile gage of the '546 patent provides improved accuracy and convenience in this conventional set-up, both the gage and the grinding wheel must be moved longitudinally along the roll for grinding and measuring operations. In addition to the deficiencies mentioned above concerning such conventional grinding apparatus and procedures, mounting of a relatively large and heavy roll within longitudinally spaced headstock and tailstock members often allows for additional error or wobbling along the longitudinal axis of the roll to enter into the grinding process, thereby further limiting the overall accuracy and resulting eccentricity of the roll. While this profile gage is quite accurate in measuring the condition of the roll surface, it does not measure angular deviation along the longitudinal axis of the roll to correct for eccentric rotation of the roll or to determine the concentricity of the outer surface about its true axis of rotation.
U.S. Pat. No. 4,958,442, which issued to R. Eckhardt, concerns a measuring device designed specifically for measuring the diameter of rolls on roll grinders. The Eckhardt device is an example of a large caliper measuring device including a boom, rotatable arm, guide arm, and a pair of measuring probes attached to measuring support bars mounted on the cross-beam and movable in a vertical direction. Eckhardt further discusses prior art devices which required that the longitudinal axis of the roll be situated at a predetermined level, because only a single measuring arm was available for movement. Another prior art device was discussed as including two measuring arms, but still requiring that the longitudinal axes of the rolls be maintained in a known position. While the Eckhardt device allegedly provides a measuring device which allows arbitrary position of the longitudinal axis of the roll, it cannot provide an accurate reading of the roundness of the roll including a measurement of concentricity, and requires a vertical column, boom and other supporting elements which would tend to interfere with grinding or machining operations.
U.S. Pat. No. 4,916,824, which issued to H. Shimazutsu, et al., allegedly addresses the problems encountered with utilizing a parallel detector way held against the ends of a roll by locating arms, and the errors caused by deflection of the detector way in use. Like the Hoover patent discussed above, the Shimazutsu, et al. device is utilized to determine the outer profile or crown of the working surface of a roll, yet has no way of determining or monitoring the center of the rotating roll to determine true roundness and concentricity. While Shimazutsu et al. recognize the inherent errors inherently imposed by deflections of longitudinal ways, and attempt to address such problems, they do not provide an apparatus or method for measuring and machining roll roundness as required by more demanding product tolerances.
Another roll measuring device is shown in U.S. Pat. No. 4,949,468, which issued to P. Kohler. The Kohler device is specifically designated for measuring the diameter of a rotationally symmetric body, and utilizes a measuring jaw that wraps around the peripheral surface and features a pair of arms with a stylus on the free ends of those arms. The Kohler device similarly requires a longitudinal way, relies upon the rotational symmetry of the roll to be measured, and is directed merely to obtaining a measurement of the diameter of the roll. While diameter accuracy is certainly important in large rolls such as used in steel mills, paper mills, and the like, a measurement of diameter does not provide the data required to determine the roundness and concentricity of the roll.
Roundness of a roll has also often been determined by comparison with a master round having a cross-section comparable to that of the roll and located physically close enough for direct comparison by utilizing a pair of closely adjacent probes. The problem with such set-ups is that it is often difficult to locate the master round closely adjacent to the portion of a roll to be measured, as well as requiring a specific size master round for each part size. Another problem with this procedure is that it does not measure the angular motion of the axis of rotation of the roll.
Another method utilized to measure out-of-roundness is known as the bench-center method. Particularly, the part to be measured is mounted on a mandrel with center holes for rotation on the bench, whereby accurate measurements are made of the outer surface. Problems with this method are that the part must have center holes or be adaptable to mounting on a mandrel with center holes. Such mounting is obviously cumbersome in cases of very large and heavy rolls. Additionally, measurement accuracy is effected by the shape and angle of the centers and center holes, location and alignment of the centers and the center holes, lubrication of the center, and straightness of the part surface itself Moreover, these variable factors must be controlled to a greater degree than the roundness accuracy desired.
Consequently, while requirements for closer tolerances and finished product gages have become much more demanding, processes and devices for machining and measuring the rolls used to produce these materials has not kept pace. Heretofore, there has not been available an apparatus or method for precisely machining and measuring roll roundness on the outer surface of relatively large rolls, wherein accurate and repeatable measuring and precise machining can be accomplished in an efficient and timely manner. Prior grinding and measuring techniques are limited in accuracy and uniformity and are unable to provide roll roundness accuracies sufficient to meet these increasing requirements.